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Produce => Pests & Diseases => Topic started by: Tee Gee on April 22, 2021, 23:11:35

Title: Microwaving compost?
Post by: Tee Gee on April 22, 2021, 23:11:35
Over the years I have read articles here about sterilising compost using a microwave  and after a quick search I can’t find any that specifically describes how to do it e.g. cooking times (if that is the correct description) relative to the quantities being sterilised?

We are replacing our old microwave oven because the turntable does not turn, but all the other facilities work OK so I thought I might give it a try.

The ovens power is 800 watts.

Do any of you have any tried and tested methods of how to go about it?

I just want to ensure that I don’t zap the compost too much as I know from experience what this can do to foodstuff.

I look forward to you recipes! 

Title: Re: Microwaving compost?
Post by: pumpkinlover on April 23, 2021, 08:16:31
We were given a microwave which had a fault with the grill so I've using it for compost making. This method I use has not been researched but it seems to kill weed seeds.

I use 3 of the trays Chinese take aways use filled with compost for 4 minutes if seed  compost and 3 minutes if potting. The take away trays have been in use for several years which is good as I don;t eat Chinese take aways.
Title: Re: Microwaving compost?
Post by: Obelixx on April 23, 2021, 14:25:06
Compost here grows weeds so I looked up how to sterilise it and found this on the Gardening Know How website.   I've done it a couple of times for seeds which are really small or take their own sweet time to germinate:-

Sterilizing Soil with a Microwave Another option to sterilize soil is to use the microwave. For the microwave, fill clean microwave-safe containers with moist soil– quart size with lids are preferable (no foil). Add a few ventilation holes in the lid. Heat the soil for about 90 seconds per every couple pounds on full power. Note: Larger microwaves can generally accommodate several containers. Allow these to cool, placing tape over the vent holes, and leave until ready to use. Alternatively, you can place 2 pounds (1 kg.) of moist soil in a polypropylene bag. Put this in the microwave with the top left open for ventilation. Heat the soil for 2 to 2 1/2 minutes on full power (650 watt oven). Close the bag and allow it to cool before removing.

Read more at Gardening Know How: Tips To Sterilize Potting Soil, Garden Soil And Soil For Seeds
Title: Re: Microwaving compost?
Post by: Beersmith on April 23, 2021, 20:40:37
Good question.

Good answers.

Thanks all.
Title: Re: Microwaving compost?
Post by: pumpkinlover on April 24, 2021, 08:19:12
I forgot to mention that I have to check the compost first for insect and worm life!
Title: Re: Microwaving compost?
Post by: Vinlander on April 24, 2021, 11:36:27
I forgot to mention that I have to check the compost first for insect and worm life!

Yes, few things are more shameful & annoying  :BangHead: than finding you've cooked a centipede - probably the best underground friend a gardener can have - high on the friends list with robins and ladybirds.

I spend several minutes picking through each batch of compost to be nuked, and in the process I also save a few friendly spiders and worms, but I've given up chasing the woodlice to where I can't see them.

I use a pair of 6 litre microwave pots (99p each from the 99p store) so I've always got some in reserve during a big job like potting up chitted aubergines, peppers & toms (I always nuke last year's stuff so 10-20 minutes on full power depending on how dodgy it looks). If you don't use it all then fungi will creep in - takes about 2 weeks but it can be re-nuked.

I usually include cockapoo pellets (poultry not dogs) in the batch - for greedy chits - doesn't smell and it doesn't seem to fungus any quicker.

OTOH Garden soil will make the compost smell very strongly as it cooks - so if you use the kitchen microwave do everything in your power to keep garden soil (including John Innes) out. I found my personal MO in the street (gomi) but if it might have been rained on, don't plug it in for at least a week or so.

I use readymeal containers too - but only for chitting - I nuke the whole pre-seed package - nearly closed container with platform (bottom 8mm of damaged trays + flat section from damaged lids) and damp tissue all in place (if using kitchen roll pierce it down the midline or it will billow up - choose really rubbish stuff - minimum wet-strength makes it easier to get the chits' roots out - the cheapest range in supermarkets is much worse [ie. better] than what's in the pound stores).

The best trays by far are the ones from City Kitchen - will last a lifetime (and the meals are better than most - though their Katsu curry hasn't been the same since they took the raw spring onion out - but just pop your own in and it's still good).


PS. In an emergency you can microwave damp (not sopping) stuff in a sturdy cardboard box - I've used well-shaken-out  old washing powder boxes many times (cut down to fit upright through the door).
Title: Re: Microwaving compost?
Post by: Tee Gee on April 24, 2021, 12:48:43
Thanks everyone some good information there for me to follow.

This morning. I made up 90 litres of Ji 3 and 60 litres of Ji2 but did not nuke it!

My plan is to only nuke the quantities I need for specific tasks, for example when sowing or pricking out. I will use un-nuked compost in large pots and planters,which is effectively IMHO the same as planting out into a border/ bed.

This method should also make it easier to locate friendly soil life before nuking.
So once again thanks for the info.  Tg
Title: Re: Microwaving compost?
Post by: Tee Gee on June 10, 2021, 16:34:15
Finally got around to organising myself.

Based on the info you guys kindly sent to me.

The Microwave is in the heated greenhouse and is an 800 watt model as opposed to the 650watt one used in your examples.

I have altered a food container by drilling holes in the lid to cater for ventilation.

I have weighed the container full of compost in order to calculate 'cooking times' (it holds 0.6 kg)

I did some simple maths to calculate the 'cooking time' for 0.6 kg in a 800watt microwave and calculated it should be around 1½ minutes per bowl full.

As I am most likely going to be using this set up for seed/cutting compost, I established that I can fill two punnets of the type I use for seed sowing.

(see images below)